1. Field of the Invention
The present invention relates to a display-driving device and a display-driving method for driving a panel type display such as a liquid crystal display, a plasma display, and a display for displaying a picture image corresponding to an image signal on an optical waveguide plate by controlling leakage light at a predetermined position of the optical waveguide plate by controlling the displacement action of an actuator element in a direction to make contact or separation with respect to the optical waveguide plate in accordance with an attribute of the image signal to be inputted (conveniently referred to as xe2x80x9celectrostrictive type displayxe2x80x9d).
2. Description of the Related Art
Those hitherto known as displays include display devices such as cathode ray tubes (CRT), liquid crystal displays, and plasma displays.
Those known as the cathode ray tube include, for example, ordinary television receivers and monitor units for computers. Although the cathode ray tube has a bright screen, it consumes a large amount of electric power. Further, the cathode ray tube involves a problem that the depth of the entire display device is large as compared with the size of the screen. Further, for example, the cathode ray tube involves drawbacks in that the resolution is decreased in the circumferential areas of the display images, the image or the graphic is distorted, there is no memory function, and it is impossible to present display in a large scale.
The reason for the foregoing phenomenon is as follows. That is, in the case of the cathode ray tube, the electron beam emitted from the electron gun is greatly deflected. Therefore, the light emission point (beam spot) is expanded at portions at which the electron beam reaches the fluorescent screen of the Braun tube in an inclined manner, and thus the image is displayed in an inclined manner. For this reason, strain occurs on the display image. Moreover, there is a limit for the maintenance to keep a large space at the inside of a Braun tube to be in a vacuum.
On the other hand, the panel type display, for example, the liquid crystal display is advantageous in that the entire device can be miniaturized, and the display consumes a small amount of electric power. The plasma display and the electrostrictive type display can be miniaturized, because the display section itself does not have a large volume, in the same manner as the liquid crystal display as described above. They are advantageous in that there is no trouble in viewing the screen, because the display surface is flat. Especially, the AC type plasma display and the electrostrictive type display are also advantageous in that the refresh memory is unnecessary owing to the memory function of the cell.
An object of the present invention is to provide a display-driving device and a display-driving method which make it possible to effectively reduce electric power consumption and achieve high brightness in a panel type display as described above.
Another object of the present invention is to provide a display-driving device and a display-driving method which make it possible to effectively reduce electric power consumption and achieve high brightness in gradation control based on subfield driving.
Still another object of the present invention is to provide a display-driving device and a display-driving method which make it possible to reduce the total number of subfields and effectively reduce electric power consumption in gradation control based on subfield driving.
According to the present invention, there is provided a display-driving device for a display comprising a driving section including a large number of picture elements arranged in a matrix form for displaying a picture image corresponding to a supplied image signal; the display-driving device comprising a first driving circuit for selecting the picture elements at least in one row unit, a second driving circuit for outputting display information composed of an ON signal and an OFF signal to a selected row, and a signal control circuit for controlling the first and second driving circuits; wherein assuming that a display period for one image is one field in order to perform gradation control based on at least a temporal modulation system, the signal control circuit determines, in the one field, a light emission start timing and a light emission maintenance period having a variable length irrelevant to a selection/unselection state of the concerning picture element depending on a gradation level of the selected picture element.
Assuming that the display period for one image is one field, the light emission start time of the concerning picture element and the light emission maintenance period having the variable length irrelevant to the selection/unselection state of the concerning picture element are determined in the one field depending on the gradation level of the selected picture element, in accordance with the control performed by the signal control circuit. Accordingly, the light emission is started for the concerning picture element substantially in synchronization with the light emission start timing, and the light emission state is maintained over the light emission maintenance period.
This arrangement makes it possible to effectively reduce the electric power consumption as compared with other driving systems in which one field is divided into a plurality of subfields, and forcible reset is performed for each of the subfields (as adopted, for example, for the plasma display). Further, the light emission state is maintained over the light emission maintenance period. Therefore, it is also possible to realize the improvement in brightness.
In the display-driving device constructed as described above, it is also preferable that one selection period and display cycles of a number corresponding to a maximum gradation level are allotted in the one field; each of the display cycles is composed of an unselection period and a reset period; and the signal control circuit is operated such that the concerning picture element is in a light emission state when the ON signal indicating light emission is inputted during the selection period, or the concerning picture element is in a light off state when the OFF signal indicating light off is inputted during the reset period in the display cycle.
Accordingly, assuming that the selection period is allotted to the head of the one field, one display cycle is selected, or a plurality of display cycles are continuously selected from the head of the one field depending on the gradation level of the concerning picture element. The ON signal is outputted at the head of the selected display cycle, and the OFF signal is outputted in the reset period of the display cycle next to the selected display cycle. In other words, the head of the selected display cycle is the light emission start timing, and the period corresponding to the selected display cycle is the light emission maintenance period.
In this arrangement, only one cycle is used for the light emission and the light off for the concerning picture element in the one field. Accordingly, it is possible to effectively reduce the electric power consumption. Further, the good linearity is obtained for the gradation and the brightness, and thus it is possible to make highly accurate gradational expression. Furthermore, the efficiency of the light emission time is also enhanced.
In the display-driving device constructed as described above, it is also preferable that signal levels are determined for the unselection period and the reset period so that the light emission state of the concerning picture element is maintained during the light emission maintenance period; and signal levels are determined for the selection period and the unselection period so that the light off state of the concerning picture element is maintained during any period other than the light emission maintenance period. In this arrangement, it is easy to achieve the maintenance of light emission during the light emission maintenance period and the maintenance of light off during the period other than the light emission maintenance period. Thus, it is possible to reliably perform the cycle including only one time of light emission and light off in the one field as described above.
In the display-driving device constructed as described above, it is also preferable that display cycles of a number corresponding to a maximum gradation level and one reset period are allotted in the one field; each of the display cycles is composed of a selection period and an unselection period; and the signal control circuit is operated such that the concerning picture element is in a light emission state when the ON signal indicating light emission is inputted during the selection period, or the concerning picture element is in a light off state during the reset period.
Accordingly, assuming that the reset period is allotted to the rear end of the one field, one display cycle is selected, or a plurality of display cycles are continuously selected from the rear end of the one field depending on the gradation level of the concerning picture element. The ON signal is outputted at the head of the selected display cycle, and the OFF signal is outputted in the reset period at the rear end.
Also in this arrangement, only one cycle is used for the light emission and the light off for the concerning picture element in the one field. Accordingly, it is possible to effectively reduce the electric power consumption. Further, the good linearity is obtained for the gradation and the brightness, and thus it is possible to make highly accurate gradational expression. Furthermore, the efficiency of the light emission time is also enhanced. Especially, the brightness can be sufficiently maintained over the light emission maintenance period for the concerning picture element, because the selection period exists for every selected display cycle.
In the display-driving device constructed as described above, it is also preferable that signal levels are determined for the selection period and the unselection period so that the light emission state of the concerning picture element is maintained during the light emission maintenance period. Accordingly, it is easy to achieve the maintenance of light emission during the light emission maintenance period and the maintenance of light off during the period other than the light emission maintenance period. Thus, it is possible to reliably perform the cycle including only one time of light emission and light off in the one field.
In the display-driving device constructed as described above, it is also preferable that an odd/even-adjusting cycle including a unit unselection period having a predetermined length between two selection periods, and display cycles of a number corresponding to a maximum gradation level are allotted in the one field; and each of the display cycles is provided with a redundant unselection period having a length which is twice the predetermined length and a reset period.
In this arrangement, for example, it is assumed that eight gradations are expressed in the one field. If the one field is constructed by using only the unit display cycle, it is necessary to perform selective scanning eight times for one row. However, when the display cycles, each of which is provided with the redundant unselection period having the length twice the predetermined length, are allotted, it is enough to perform selective scanning five times for one row. Thus, it is possible to reduce the cycles (row scanning cycles) for selecting one row. This results in the reduction of the electric power consumption.
Further, this also results in the high brightness of the selected picture element, because the light emission state is maintained during the redundant unselection period.
When the gradation level of the concerning picture element is odd, the light emission start timing is set to be substantially in synchronization with the head selection period of the odd/even-adjusting cycle; while when the gradation level of the concerning picture element is even, the light emission start timing is set to be substantially in synchronization with the rear end selection period of the odd/even-adjusting cycle.
In the display-driving device constructed as described above, it is also preferable that display cycles of a number corresponding to a maximum gradation level, and an odd/even-adjusting cycle including a unit unselection period having a predetermined length between two reset periods are allotted in the one field; and each of the display cycles is provided with a selection period and a redundant unselection period having a length which is twice the predetermined length.
Also in this arrangement, it is possible to reduce the row scanning cycles as described above, and it is possible to reduce the electric power consumption.
When the gradation level of the concerning picture element is odd, an end timing for the light emission maintenance period is set to be substantially in synchronization with the terminal end reset period of the odd/even-adjusting cycle; while when the gradation level of the concerning picture element is even, the end timing for the light emission maintenance period is set to be substantially in synchronization with the head reset period of the odd/even-adjusting cycle.
In the display-driving device constructed as described above, it is also preferable that at least one unit display cycle including a unit unselection period having a predetermined length, and at least one redundant display cycle are allotted in the one field; and the redundant display cycle is provided with a redundant unselection period having a length which is n-times the predetermined length (n is an integer of not less than 2).
In this arrangement, for example, it is assumed that eight gradations are expressed in the one field. It is enough to perform selective scanning five times for one row. Thus, it is possible to greatly reduce the row scanning cycles. As a result, it is possible to realize the reduction of electric power consumption and the high brightness.
In the display-driving device constructed as described above, it is also preferable that the following expressions are satisfied:
Z=(quotient of X/n)xe2x88x921
Y=Xxe2x88x92Zxc3x97n
[total number of subfields (Y+Z)=(X/nxe2x88x921)+n]
provided that a maximum gradation level is X, a number of unit display cycles is Y, and a number of redundant display cycles is Z. In this arrangement, the total number of subfield exactly corresponds to the row scanning cycles described above. Therefore, a combination to minimize the total number of subfields necessarily exists. When such a combination is adopted, then it is possible to reduce the electric power consumption more effectively, and it is possible to mitigate the load on the scanning circuit.
Preferably, xe2x80x9caxe2x80x9d individuals of selection periods are allotted to the respective display cycles from a head of the one field, and xe2x80x9cbxe2x80x9d individuals of reset periods are allotted to the respective display cycles from a rear end of the one field; wherein the following expression is satisfied:
a+b=Y+Z+1.
Accordingly, it is possible to make a variety of gradational expressions. In this arrangement, in the case of b=n, all of the gradations included in the maximum gradation level can be expressed. However, assuming that there is given b=nxe2x88x921, one or several gradation levels may be curtailed. This reduces the row scanning cycles, and hence it is possible to realize the low electric power consumption.
In the display-driving device constructed as described above, it is also preferable that the unit display cycle and the redundant display cycle are allotted by using a combination which corresponds to a minimum total number of subfields of total numbers of subfields corresponding to a maximum gradation level obtained by arbitrarily combining the unit display cycle and the redundant display cycle.
For example, if the maximum gradation level is 16, the total number of subfields is 15 in the case of only the unit display cycle, 9 in the case of a combination of the unit display cycle and the 2-fold redundant display cycle, 7 in the case of a combination of the unit display cycle and the 4-fold redundant display cycle, or 9 in the case of a combination of the unit display cycle and the 8-fold redundant display cycle. In this case, the combination of the unit display cycle and the 4-fold redundant display cycle is selected, in which the total number of subfields is minimum.
As a result, it is possible to reduce the electric power consumption more effectively, and it is possible to mitigate the load on the scanning circuit as having been described above.
In the display-driving device constructed as described above, it is also preferable that the one field includes therein a first subfield block composed of at least one redundant display cycle and a second subfield block composed of at least one unit display cycle; and a forcible reset period is provided between the first and second subfield blocks.
Owing to the use of the redundant display cycle in the first subfield block, it is possible reduce the number of row scanning cycles, and it is possible to realize the reduction of electric power consumption. Especially, owing to the provision of the forcible reset period, it is possible to give a signal sufficient to quench the picture element during the period.
In the display-driving device constructed as described above, it is also preferable that the second subfield block is composed of at least one redundant display cycle and at least one unit display cycle.
In this arrangement, it is also possible to reduce the number of row scanning cycles in the second subfield block. Therefore, it is possible to realize the further reduction of electric power consumption.
In the display-driving device constructed as described above, it is also preferable that the display comprises an optical waveguide plate for introducing light thereinto, and the driving section provided opposingly to one plate surface of the optical waveguide plate and including a number of actuator elements arranged corresponding to the large number of picture elements, for displaying, on the optical waveguide plate, the picture image corresponding to the image signal by controlling leakage light at a predetermined portion of the optical waveguide plate by controlling displacement action of each of the actuator elements in a direction to make contact or separation with respect to the optical waveguide plate in accordance with an attribute of the image signal to be inputted.
In the present invention, it is desirable that the first and second driving circuits have the following features.
(1) The actuator element undergoes the capacitive load. Therefore, considering the fact that the capacitive load is subjected to the driving, it is desirable that the partial voltage ratio, which is applied to the capacitive load, is not less than 50%, for example, at the time of completion of voltage (ON voltage) application for allowing the actuator element to make the bending displacement.
(2) In order to obtain an displacement amount of the actuator element which makes it possible to express the ON state and the OFF state of the picture element, it is desirable that an voltage output of not less than 20 V can be provided.
(3) It is desirable to consider the fact that the direction of the output current is recognized to be bidirectional.
(4) It is desirable that the load concerning the two-electrode structure in the row direction and the column direction can be subjected to the driving.
Especially, it is also preferable that the actuator element comprises a shape-retaining layer, an operating section having at least a pair of electrodes formed on the shape-retaining layer, a vibrating section for supporting the operating section, and a fixed section for supporting the vibrating section in a vibrating manner; wherein the display comprises a displacement-transmitting section for transmitting the displacement action of the actuator element to the optical waveguide plate, the displacement action being generated by voltage application to the pair of electrodes.
In the present invention, the term xe2x80x9cactuator element having the shape-retaining layerxe2x80x9d indicates an actuator element which has at least two or more displacement states at an identical voltage level.
Accordingly, all of the light, which is introduced, for example, from the end of the optical waveguide plate, is totally reflected at the inside of the optical waveguide plate without being transmitted through the front and back surfaces of the optical waveguide plate (light off state), by regulating the magnitude of the refractive index of the optical waveguide plate. In this light off state, for example, when the displacement-transmitting section contacts with the back surface of the optical waveguide plate at a distance of not more than the wavelength of the light, then the light, which has been totally reflected, is transmitted to the surface of the displacement-transmitting section contacting with the back surface of the optical waveguide plate. The light, which has once reached the surface of the displacement-transmitting section, is reflected by the surface of the displacement-transmitting section, and the light behaves as scattered light. A part of the scattered light is reflected again at the inside of the optical waveguide plate. However, almost all of the scattered light is not reflected by the optical waveguide plate, and the light is transmitted through the front surface of the optical waveguide plate (light emission state).
As described above, it is possible to control the presence or absence of light emission (leakage light) at the front surface of the optical waveguide plate, depending on the presence or absence of the contact of the displacement-transmitting section disposed at the back of the optical waveguide plate. In this case, one unit for allowing the displacement-transmitting section to make the displacement action in the direction to give contact or separation with respect to the optical waveguide plate may be regarded as one picture element. Thus, a picture image (for example, characters and graphics) corresponding to an image signal can be displayed on the front surface of the optical waveguide plate in the same manner as in the cathode ray tube and the liquid crystal display, by arranging a large number of such picture elements in a matrix form, and controlling the displacement action of each of the picture elements in accordance with an attribute of the inputted image signal.
The actuator element having the shape-retaining layer has the following features.
(1) The threshold characteristic concerning the change from the light off state to the light emission state is steep as compared with the case in which no shape-retaining layer exists. Accordingly, it is possible to narrow the deflection width of the voltage, and it is possible to mitigate the load on the circuit.
(2) The difference between the light emission state and the light off state is distinct, resulting in improvement in contrast.
(3) The dispersion of threshold value is decreased, and an enough margin is provided for the voltage setting range.
It is desirable to use, as the actuator element, an actuator element which makes, for example, upward displacement (giving the separated state upon no voltage load and giving the contact state upon voltage application) because of easiness of control. Especially, it is desirable to use an actuator element having a structure including a pair of electrodes on its surface. It is preferable to use, for example, a piezoelectric/electrostrictive layer and an anti-ferroelectric layer as the shape-retaining layer.
In the display-driving device constructed as described above, it is also preferable that the driving section is formed with switching elements corresponding to the actuator elements respectively; and the displacement action of the actuator element is controlled by means of ON/OFF control effected by the switching element.
Accordingly, the large number of arranged actuator elements are selected in the unit of row on the basis of the input of the image signal, and the display information (voltage signal) concerning the selected row is supplied.
Usually, the voltage signal is also supplied to the actuator elements concerning the unselected row irrelevant to the selected row. However, in the case of the display according to the present invention, the actuator elements concerning the unselected row are operated as follows. That is, the unselected row can be prevented from the supply of the display information by turning off the corresponding switching elements. Accordingly, it is unnecessary to drive the picture elements (actuator elements) concerning the unselected row. Thus, it is possible to effectively reduce the electric power consumption.
The electrostatic capacity of the actuator element is small, and the CR time constant depending on the wiring resistance and the switching ON resistance is small. Therefore, when the switching element is turned on, the actuator elements concerning the selected row are quickly charged. When the switching element is turned off thereafter, the connected section between the display information supply line (signal line) and the actuator element is in a state of extremely high impedance, i.e., in a state approximately equivalent to the open state. This means the fact that the resistance becomes extremely large.
Therefore, the CR time constant also becomes extremely large.
Accordingly, even when the switching element is turned off, the supply of the display information (application of the voltage signal) to the actuator element is maintained. Therefore, the concerning actuator element continuously maintains the displacement amount of not less than a certain amount. Thus, the ON state of the concerning picture element is maintained.
As described above, the actuator element concerning the unselected row is maintained in the open state while being charged. The displacement amount, which has been given upon the selection of the row, can be maintained for a certain period of time in the state of being applied with no signal. Therefore, it is possible to effect the light emission of the picture element during the unselection period. Accordingly, it is possible to realize the high brightness.
The respective switching elements can be formed on the driving section (either on the principal surface or on the back surface thereof). Therefore, it is unnecessary to form any large wiring pattern on the driving section. Thus, it is possible to simplify the wiring arrangement.
Unlike the liquid crystal display (TFT-LCD), the respective switching elements can be installed in the space (at the place) irrelevant to the optical path. The respective switching elements can be provided on the back surface of the driving section. Accordingly, it is possible to provide a large numerical aperture of the picture element, and thus it is possible to improve the brightness.
It is preferable that the switching element is composed of a varistor. In this arrangement, an extremely excellent hysteresis characteristic is obtained when the actuator element is allowed to perform the displacement action. Thus, it is possible to obtain an memory effect as providing the approximately complete shape maintenance.
According to another aspect of the present invention, there is provided a display-driving method for a display comprising a driving section including a large number of picture elements arranged in a matrix form for displaying a picture image corresponding to a supplied image signal; the display-driving method comprising the steps of selecting the picture elements at least in one row unit; outputting display information composed of an ON signal and an OFF signal to a selected row; and performing gradation control based on at least a temporal modulation system; wherein assuming that a display period for one image is one field, a light emission start timing and a light emission maintenance period having a variable length irrelevant to a selection/unselection state of the concerning picture element are determined in the one field depending on a gradation level of the selected picture element.
In this method, it is also preferable that one selection period and display cycles of a number corresponding to a maximum gradation level are allotted in the one field; each of the display cycles is composed of an unselection period and a reset period; and the concerning picture element is in a light emission state when the ON signal indicating light emission is inputted during the selection period; or the concerning picture element is in a light off state when the OFF signal indicating light off is inputted during the reset period in the display cycle.
In this case, it is also preferable that signal levels are determined for the unselection period and the reset period so that the light emission state of the concerning picture element is maintained during the light emission maintenance period; and signal levels are determined for the selection period and the unselection period so that the light off state of the concerning picture element is maintained during any period other than the light emission maintenance period.
Further, it is also preferable that display cycles of a number corresponding to a maximum gradation level and one reset period are allotted in the one field; each of the display cycles is composed of a s election period and an unselection period; and the concerning picture element is in a light emission state when the ON signal indicating light emission is inputted during the selection period; or the concerning picture element is in a light off state during the reset period.
In this case, it is also preferable that signal levels are determined for the selection period and the unselection period so that the light emission state of the concerning picture element is maintained during the light emission maintenance period.
In the method described above, it is also preferable that an odd/even-adjusting cycle including a unit unselection period having a predetermined length between two selection periods, and display cycles of a number corresponding to a maximum gradation level are allotted in the one field; and each of the display cycles is provided with a redundant unselection period having a length which is twice the predetermined length and a reset period.
When the gradation level of the concerning picture element is odd, the light emission start timing is set to be substantially in synchronization with the head selection period of the odd/even-adjusting cycle; while when the gradation level of the concerning picture element is even, the light emission start timing is set to be substantially in synchronization with the rear end selection period of the odd/even-adjusting cycle.
In the method described above, it is also preferable that display cycles of a number corresponding to a maximum gradation level, and an odd/even-adjusting cycle including a unit unselection period having a predetermined length between two reset periods are allotted in the one field; and each of the display cycles is provided with a selection period and a redundant unselection period having a length which is twice the predetermined length.
When the gradation level of the concerning picture element is odd, an end timing for the light emission maintenance period is set to be substantially in synchronization with the terminal end reset period of the odd/even-adjusting cycle; while when the gradation level of the concerning picture element is even, the end timing for the light emission maintenance period is set to be substantially in synchronization with the head reset period of the odd/even-adjusting cycle.
In the method described above, it is also preferable that at least one unit display cycle including a unit unselection period having a predetermined length, and at least one redundant display cycle are allotted in the one field; and the redundant display cycle is provided with a redundant unselection period having a length which is n-times the predetermined length (n is an integer of not less than 2).
In this case, it is also preferable that the following expressions are satisfied:
Z=(quotient of X/n)xe2x88x921
Y=Xxe2x88x92Zxc3x97n
[total number of subfields (Y+Z)=(X/nxe2x88x921)+n]
provided that a maximum gradation level is X, a number of unit display cycles is Y, and a number of redundant display cycles is Z.
It is also preferable that xe2x80x9caxe2x80x9d individuals of selection periods are allotted to the respective display cycles from a head of the one field, and xe2x80x9cbxe2x80x9d individuals of reset periods are allotted to the respective display cycles from a rear end of the one field; wherein the following expression is satisfied:
a+b=Y+Z+1.
In this case, there may be given b=n, or b=nxe2x88x921.
Especially, it is preferable that the unit display cycle and the redundant display cycle are allotted by using a combination which corresponds to a minimum total number of subfields of total numbers of subfields corresponding to a maximum gradation level obtained by arbitrarily combining the unit display cycle and the redundant display cycle.
In the method described above, it is also preferable that the one field includes therein a first subfield block composed of at least one redundant display cycle and a second subfield block composed of at least one unit display cycle; and a forcible reset period is provided between the first and second subfield blocks.
In this case, it is also preferable that the second subfield block is composed of at least one redundant display cycle and at least one unit display cycle.
In the driving method described above, it is also preferable that the gradation control is performed for the picture element by means of ON/OFF control effected by a switching element. In this case, it is preferable that a varistor is used as the switching element.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.